rcu: Make synchronize_rcu_mult() check for duplicates
Currently, doing synchronize_rcu_mult(call_rcu, call_rcu) might
(or might not) wait for two RCU grace periods. One approach is
of course "don't do that!", but in CONFIG_PREEMPT=n kernels,
synchronize_rcu_mult(call_rcu, call_rcu_sched) does exactly that.
This results in an ugly #ifdef in sched_cpu_deactivate().
This commit therefore makes __wait_rcu_gp() check for duplicates,
which in turn allows duplicates to be passed to synchronize_rcu_mult()
without risk of waiting twice on the same type of grace period.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 82a5aa1..123a9c4 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -379,6 +379,7 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
struct rcu_synchronize *rs_array)
{
int i;
+ int j;
/* Initialize and register callbacks for each flavor specified. */
for (i = 0; i < n; i++) {
@@ -390,7 +391,11 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
}
init_rcu_head_on_stack(&rs_array[i].head);
init_completion(&rs_array[i].completion);
- (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
+ for (j = 0; j < i; j++)
+ if (crcu_array[j] == crcu_array[i])
+ break;
+ if (j == i)
+ (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
}
/* Wait for all callbacks to be invoked. */
@@ -399,7 +404,11 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
(crcu_array[i] == call_rcu ||
crcu_array[i] == call_rcu_bh))
continue;
- wait_for_completion(&rs_array[i].completion);
+ for (j = 0; j < i; j++)
+ if (crcu_array[j] == crcu_array[i])
+ break;
+ if (j == i)
+ wait_for_completion(&rs_array[i].completion);
destroy_rcu_head_on_stack(&rs_array[i].head);
}
}